Biorationals and Synthetic Insecticides for Controlling FallArmyworm and Their Influence on the Abundance andDiversity of Parasitoids

Abstract

Spodoptera frugiperda(fall armyworm, FAW) is a significant economic pest of maize inUganda. Many Ugandan maize farmers employ synthetic insecticides as their main form of controldespite the negative impacts of these chemicals. We tested the effectiveness ofBeauveria bassiana;General Biopesticide Cocktail (mixture ofB. bassiana,M. anisopliae,Isaria fumosoroseus,LecanicilliumlecaniandPurporeocillium lilacanusthree strains ofMetarhizium anisopliae, Nimbecidine®(azadirachtin0.03%EC), and Roket®(cypermethrin 4% and profenofos 40%); and Amdocs®(emamectin ben-zoate 2% and abamectin 1%) on fall armyworm and parasitoids, respectively, in 2020 and 2021. Thetreatments with the greatest decrease in leaf damage and infestation were Amdocs®and Roket®,followed by Nimbecidine®. The biopesticides were not always more effective than the untreatedcontrol, though; their efficacy was often lower than that of the synthetic and botanical pesticides. Werecovered one egg parasitoid,Telenomus remus, and seven egg and egg-larval parasitoids (Coccygidiumluteum,Coccygidiumsp.,Cotesia icipe,Chelonussp.,Micranisasp.,Charopscf.diversipes, and an uniden-tified Tachinidae). Among these,C.cfdiversipes,Chelonussp.,C. luteum,C. icipeand the Tachinidaewere the most abundant. Parasitism was low, averaging 10% for egg masses and 5.3% for larvae.Application of synthetic pesticides and Nimbecidine®often resulted in higher yield when comparedwith the untreated control. In general, a low population of parasitoids was observed. Althoughthe parasitoid population reduced in plots treated with Amdocs®and Roket®, the percentage ofparasitism of FAW was not affected. In some instances, higher yields were realized in untreatedcontrol when compared with the treated plots. Pest management practices more compatible withbiological control need to be considered for the management of fall armyworm.